ABSTRACT The World Trade Center (WTC) Health Registry is the largest post-disaster registry in U.S. history. The Registry follows a diverse cohort of over 71,000 persons who performed 9/11-related rescue/recovery work, or who lived, worked or attended school in lower Manhattan on 9/11/2001. The Registry aims to identify the long- term physical and mental health effects of the WTC disaster. We propose five Specific Aims for the Extension of the Registry. (1) Maintain the Registry as a valuable public health resource to allow health professionals to track and investigate possible trends in illness and recovery. Aim 1 will sustain critical Registry infrastructure through communications and tracing activities to maintain contact with enrollees and maximize those with valid contact information; timely communications with enrollees to address concerns and keep them engaged and interested in participating in future research; and outreach activities to boost response to Registry studies. (2) Expand knowledge about the long-term health effects of 9/11 by facilitating medical, public health or emergency preparedness research, or other scientific research relevant to the WTC Health Program with special emphasis on impacts to those who lived, worked or attended school in the disaster area. Aim 2 entails conducting priority epidemiological analyses using data from Wave 1 (2003-04), Wave 2 (2006-08), Wave 3 (2011-12), and Wave 4 (2015-16) surveys and in-depth studies, including analyses to assess risk factors for the development or persistence of respiratory and mental health conditions; extending assessment of cancer and mortality incidence through 15 years post-9/11; investigating potential emerging health conditions through public health surveillance and follow-up studies; developing and conducting a Wave 5 survey using multiple survey modes (paper, web) to ascertain the health status and 9/11-related healthcare needs of the cohort 18- 19 years after 9/11. (3) Conduct community activities to respond to the physical and mental health concerns and specific health care needs of enrollees and other persons exposed to 9/11. Aim 3 will be achieved by disseminating Registry findings and recommendations together with information on 9/11-related services and resources to enrollees, the public and policy makers; developing and providing data resources such as de- identified Registry databases and online data tools for enrollees, the public and researchers. (4) Maintain the Treatment Referral Program to help enrollees and others find care for 9/11-related health problems. Aim 4 will be achieved by offering health care referrals to enrollees with 9/11 related health conditions and symptoms based on information from Registry surveys, evaluating the program and sharing findings with the WTC Health Program. (5) Collaborate with other WTC Heath Program entities to explore surveillance signals and treatment outcomes. The Registry will facilitate independent and collaborative 9/11-related research by providing qualified external researchers with de-identified data and access to enrollee subgroups through Registry- facilitated recruitment.